The Fight Against NOxious Emissions

George Teriakidis, Regional Business Development Manager DNV GL- Region South East Europe & Middle East

The IMO’s Tier III limits for nitrous oxide (NOX) emissions from new ships operating in emission control areas (ECAs) are one of the latest regulatory challenges for many shipowners. DNV GL answers some key questions regarding available technologies, ship design and retrofitting.

Environmental regulations have increased almost exponentially in recent years. The latest addition, the IMO Tier III limits for nitrogen oxides (NOX) emissions inside ECAs, confronts owners with an entirely new set of challenges in terms of both technology and compliance. DNV GL has developed a comprehensive set of advisory services to supplement its voluntary class notations, equipment certification and exhaust gas measurement programme, helping owners and engine manufacturers understand the implications and handle the intricacies of the planning and certification processes. Furthermore, the DNV GL brochure “DNV GL NOX Tier III Update” offers an excellent introduction to the subject. “While the so-called sulphur cap applies retroactively to all ships globally, the new NOX limits are only relevant for new ships operating inside ECAs,” clarifies Georgios Teriakidis, Regional Business Development Manager ,DNV GL- Region South East Europe, Middle East &Africa.

“However, many owners and shipyards underestimate the complexity not only of the technology required for implementation, but of the certification process as well. In particular, the documentation requirements for Tier III certification are well defined by IMO as well as the certification process which requires only one responsible applicant, whether it is the owner, shipyard, engine or after treatment manufacturer.”

The IMO Tier III limits for NOX emissions entered into force as part of MARPOL Annex VI on 1 January 2016. They require the NOX emissions from a new ship to be reduced by 80 per cent compared to an equivalent Tier I-compliant engine. The Tier III limits apply to ships keel-laid after 1 January 2016 when operating in North American and US Caribbean Sea ECA, and to ships keel-laid after 1 January 2021 when operating in the North and Baltic Seas. China, while imposing only SOX limits in its ECAs for the time being, is contemplating adding NOX eventually (refer to interview).

The IMO Tier III NOX emission limits apply to new ships inside North American and US Caribbean Sea ECA. European newbuilds will follow suit from 2021.

The new NOX limits cannot be met without specific treatment of exhaust gases. There are basically three approaches to achieving Tier III compliance: exhaust gas treatment using selective catalytic reduction (SCR) technology; exhaust gas recirculation (EGR); or alternative fuels, most notably liquefied natural gas (LNG). The best choice for a given vessel depends on the planned trading pattern, engine size and travelling speed, among other factors. “Owners should get informed as early as possible when planning a new ship, especially with regard to the main engine, because the emission control strategy they choose has far-reaching implications for the design of the machinery and the entire vessel,” Georgios Teriakidis points out.

Selective catalytic reduction

SCR is an exhaust gas after-treatment technology commonly used in diesel vehicles and industrial applications. By injecting ammonia or urea into the exhaust gas stream in the presence of a catalyst, the nitrous oxides are reduced selectively, forming water and molecular nitrogen. The SCR concept has an NOX abatement capability in excess of 80 per cent and does not compromise engine performance or influence engine design. Two configurations are available to make sure the exhaust gas temperature necessary for proper SCR function is maintained. “Transitional engine loads, for example during engine start-up, are not covered by the regulation, and emergency operation is exempted from the NOX emission control regulation,” says Teriakidis.

As an alternative fuel, liquefied natural gas (LNG) is an attractive option for both SOX and NOX compliance.

The initial investment for an SCR system is relatively high, and additional space is needed on board. To maintain the engine and exhaust system in good condition it is necessary to monitor and control fuel quality, engine load, exhaust gas temperature as well as the urea injection rate and temperature. The required urea-water solution, which must be bunkered, and periodical replacements of the catalyst elements increase the ship operating costs. On the other hand, Teriakidis emphasizes, “SCR technology is highly effective at removing NOX at most engine loads and is proven in industrial applications as well as over 300 ship installations. It is currently the most mature after-treatment technology, and DNV GL has years of experience with SCR systems.”

Exhaust gas recirculation

As a second viable method of reducing NOX emission, exhaust gas recirculation (EGR) redirects a portion of the engine’s exhaust gas back to the charge air where it replaces some of the oxygen. This lowers the combustion temperature, thereby reducing the formation of NOX. Depending on the fuel, an EGR system can be equipped with a small scrubber which cleans the recirculated gas to avoid corrosion and sooting of the combustion chamber. A wash-water treatment system and a sludge tank are required as well, and in most cases caustic soda must be carried on board for scrubber operation.

SCR takes heat: a high-pressure SCR unit is preferably placed upstream of the turbocharger turbine. Lowpressure systems can use a preheater to heat up the exhaust gas and are placed downstream of all engine components.

The technology is supported by major engine manufacturers. However, operational experience with this technology is limited, initial investment costs are relatively high, and fuel consumption can be expected to increase by approximately four per cent. The IMO is currently developing guidelines for the discharge of bleed-off water from EGR NOX emission reduction systems.

Alternative approaches

DNV GL considers LNG as one of the most viable and promising options to meet emission limits. LNG avoids SOX emissions entirely and reduces NOX emissions by 80 to 90 per cent. Tier III certification is nevertheless required, and certain technical considerations are necessary to ensure NOX compliance. LNG as a ship fuel is making headway rapidly and enjoys a positive reputation among the general public. Initial investment costs remain high, however, and LNG fuel tanks take up significant amounts of space on board.

Other alternative fuels such as methanol or ethylene are not widely used as yet. Intake air humidification, which adds water to the combustion process to lower the combustion temperature and reduce NOX formation, may achieve Tier III-compliant NOX reduction rates but has not reached technical maturity as yet.

Complexities to be taken seriously

Exhaust gas recirculation systems likewise come in two configurations differing in the location from where the exhaust gas is diverted. Depending on the fuel, a small scrubber and a wash-water treatment system can also be required

Retrofitting ships with Tier III NOX technology is extremely challenging says Teriakidis, so “any new vessel that might one day change its operational pattern or be resold should be considered to be designed with Tier III NOX abatement in mind.” Furthermore, he adds, SOX and NOX compliance should be viewed as related items: “To ensure compliance with both the SOX and the NOX emission limits in the most efficient, practical and economical manner, a complete, all-encompassing compliance strategy is absolutely critical.” The DNV GL advisory services can be invaluable in guiding the planning, selection and implementation process, the certification expert says. “And there are additional advantages to consider as well: Tier III NOX compliance comes with added benefits. A compliant vessel will potentially have a significantly better resale value and is entitled to substantial harbour fee discounts in many major ports.” AK

The IMO Tier III NOX emission limits apply to new ships inside North American and US Caribbean Sea ECA. European newbuilds will follow suit from 2021

SCR takes heat: a high-pressure SCR unit is preferably placed upstream of the turbocharger turbine. Low-pressure systems can use a pre-heater to heat up the exhaust gas and are placed downstream of all engine components.

China declares designated ECAS to tackle its air pollution challenges in major port cities

What emission regulations are currently in effect in Chinese coastal regions?

Georgios Teriakidis: On 1 January 2017 a 0.5 per cent sulphur limit in ship fuel went into effect in eleven major Chinese ports. These are located in the Pearl River delta, the Yangtze River delta and the Gulf of Bohai, each of which represents an emission control area (ECA) of its own. On 1 September, all the additional ports in the Zhejiang Province of the Yangtze River delta also implemented this limit. Within these areas ships must switch to a low-sulphur fuel within one hour of arriving at their berth, and continue using this fuel until one hour before departure.

Alternative emission reduction methods such as scrubbers or shore power are permissible as well. On 1 January 2018 the 0.5 per cent sulphur limit will enter into force in all other ports inside these three ECAs as well. One year later ships will be required to make the switch to low-sulphur fuel before entering the respective ECA.

What is unclear about this regulation?

Teriakidis: The Chinese government will reassess the situation in late 2019. Depending on the outcome, the emission restrictions might be tightened. It is conceivable that the ECAs will be enlarged, a stricter fuel sulphur limit of 0.1 per cent imposed, or that nitrous oxides (NOX) will be included based on NOX Tier III. In the latter case the Chinese ECAs would conform to Marpol Annex VI.

How is the domestic supply industry evolving with respect to ECAs?

Teriakidis:The market is definitely responding. We are already working with a handful of Chinese scrubber manufacturers. Just earlier this year we issued an approval in principle to the first exhaust gas scrubber design by Shanghai Bluesoul Environmental Technology, confirming compliance with our design rules. Other suppliers are getting ready to enter the market and may – with appropriate financial backing – even appear in the global market in the medium term.

“The documentation requirements for Tier III certification are well defined by IMO as well as the certification process which requires only one responsible applicant.”